The sensitivity of a magnetic sensor is defined by a sensitivity vector S. The sensitivity vector S needs to be calibrated in order to achieve the parallelism of its components Sx, Sy and Sz with the x, y and z axis of a reference coordinate system in which a magnetic field to be measured is present. Especially for a multi-axis magnetic field sensor, the calibration of the mutual orthogonality between the sensitivity vectors of individual sensor elements is required to achieve high accurate measurements of the magnetic field. The calibration of the sensitivity vector S requires a magnetic field source which produces a stable homogeneous magnetic field having a constant field intensity, i.e. a reference magnetic field source producing a defined magnetic field vector B. In order to fulfill this requirement, commonly a set-up with Helmholtz coils or electromagnets is used as magnetic field source.
Calibration also requires that the direction of the magnetic field vector B is aligned parallel to one of the axis of the sensor's coordinate system. However, perfect parallelism is very difficult to achieve in practice, mostly resulting in insufficient accuracy of the calibration.